From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7971FC433EF for ; Tue, 12 Jul 2022 14:49:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233725AbiGLOtb (ORCPT ); Tue, 12 Jul 2022 10:49:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230256AbiGLOt2 (ORCPT ); Tue, 12 Jul 2022 10:49:28 -0400 Received: from mail-ed1-x52f.google.com (mail-ed1-x52f.google.com [IPv6:2a00:1450:4864:20::52f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 37A714E636 for ; Tue, 12 Jul 2022 07:49:27 -0700 (PDT) Received: by mail-ed1-x52f.google.com with SMTP id w12so9682798edd.13 for ; Tue, 12 Jul 2022 07:49:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=FWdXKqvBEPZJ3mA635VvLTJkZo44UTBm15/9rGxOhDg=; b=q4cwR0kOaupYQ2Qpj3mF7Dk/O6g0HtRaBJZu4k2L11VBZhgn4mHMUmuPv0orUZ5yeK rA+adQOu8Wv1YRm3Kx4zTJisfru2GG0teDHbrgY+VZFdLA1iEMYjUSiX3HF5bQWSDEWz ZeV50FkMJlJJIN9EraEFGXXw3zvJ+mQyXAE50+Ah0dipM0Xy0+9lABmW0ANikFf3AqRp S8ln76No2VnP+k6BQ91wP5jf1SBIE+KMsFyqpWYg88cLBxWkv/QxyiVNVL0+P29fXDsm 7oxL2nRJVXbFN/mCRKwstsGEXIpQlLQuhruRFEE0gohSqoUpW5lpYCrX1ReKE9cd+GV0 U9AQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=FWdXKqvBEPZJ3mA635VvLTJkZo44UTBm15/9rGxOhDg=; b=rPHX36v6QMn25V1qd3MYpwYBCYGbvKGCBOdfT8sdqAmY+SzSjvAldTq3NTbtMa+7JT 4gpBB3oUTO6gzGOgjaSGe6/e//2RtMZhxkYUHaR0BIpUZBfhldMTy/UM0Sqwfeqob0aP UhvjcfEu03CKdYn1wAsycCEoKnpztqN4Gb5TuFFhaP7Cc1F1VObl9J4MS+jjqhAjo5tO qZZpU3cIAd6/PpMJYS61hRCZNqNtCkTpCcghFYEyBfscamNR7U3sMttGdZfhxWPsDoDl 9kA4PILFPmWfk4c+VGaQeZNUQcvIsPjDE1EYCsA+ynLq5GzQv2kxNguih6oMFznIwhvM Ybfg== X-Gm-Message-State: AJIora9NPVbbgolEy1BJLk7iWCFL/KZ5+0HUH67P71ubYUsT8ALsdxSv FBQI8QE9ANeflp+OAn0YB0yvhrID/uo= X-Google-Smtp-Source: AGRyM1skbHcyY88e6nPbA+JG6pCwg62++rGrFzZrfFhkvJ/IaMIzhiHP4OvJRmKp8sILsTZq2OsSzw== X-Received: by 2002:aa7:cc03:0:b0:435:5574:bf30 with SMTP id q3-20020aa7cc03000000b004355574bf30mr32358760edt.15.1657637365492; Tue, 12 Jul 2022 07:49:25 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id b4-20020aa7d484000000b0043a46f5fb82sm6120579edr.73.2022.07.12.07.49.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Jul 2022 07:49:25 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak Subject: [PATCH] llist: Use try_cmpxchg in llist_add_batch and llist_del_first Date: Tue, 12 Jul 2022 16:49:17 +0200 Message-Id: <20220712144917.4497-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in llist_add_batch and llist_del_first. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg. Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. No functional change intended. Signed-off-by: Uros Bizjak --- lib/llist.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/lib/llist.c b/lib/llist.c index 611ce4881a87..7d78b736e8af 100644 --- a/lib/llist.c +++ b/lib/llist.c @@ -30,7 +30,7 @@ bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, do { new_last->next = first = READ_ONCE(head->first); - } while (cmpxchg(&head->first, first, new_first) != first); + } while (!try_cmpxchg(&head->first, &first, new_first)); return !first; } @@ -52,18 +52,14 @@ EXPORT_SYMBOL_GPL(llist_add_batch); */ struct llist_node *llist_del_first(struct llist_head *head) { - struct llist_node *entry, *old_entry, *next; + struct llist_node *entry, *next; entry = smp_load_acquire(&head->first); - for (;;) { + do { if (entry == NULL) return NULL; - old_entry = entry; next = READ_ONCE(entry->next); - entry = cmpxchg(&head->first, old_entry, next); - if (entry == old_entry) - break; - } + } while (!try_cmpxchg(&head->first, &entry, next)); return entry; } -- 2.35.3